The XTextExtents and XTextExtents16 functions
perform the size computation locally and, thereby, avoid the round-trip
overhead of XQueryTextExtents and XQueryTextExtents16. Both functions
return an XCharStruct structure, whose members are set to the values
as follows.

The ascent member is set to the maximum of the ascent metrics
of all characters in the string. The descent member is set to the maximum
of the descent metrics. The width member is set to the sum of the character-width
metrics of all characters in the string. For each character in the string,
let W be the sum of the character-width metrics of all characters preceding
it in the string. Let L be the left-side-bearing metric of the character
plus W. Let R be the right-side-bearing metric of the character plus W. The
lbearing member is set to the minimum L of all characters in the string.
The rbearing member is set to the maximum R.

For fonts defined with linear
indexing rather than 2-byte matrix indexing, each XChar2b structure is
interpreted as a 16-bit number with byte1 as the most significant byte.
If the font has no defined default character, undefined characters in the
string are taken to have all zero metrics.

The XQueryTextExtents and XQueryTextExtents16
functions return the bounding box of the specified 8-bit and 16-bit character
string in the specified font or the font contained in the specified GC.
These functions query the X server and, therefore, suffer the round-trip
overhead that is avoided by XTextExtents and XTextExtents16. Both functions
return a XCharStruct structure, whose members are set to the values as
follows.

The ascent member is set to the maximum of the ascent metrics
of all characters in the string. The descent member is set to the maximum
of the descent metrics. The width member is set to the sum of the character-width
metrics of all characters in the string. For each character in the string,
let W be the sum of the character-width metrics of all characters preceding
it in the string. Let L be the left-side-bearing metric of the character plus
W. Let R be the right-side-bearing metric of the character plus W. The lbearing
member is set to the minimum L of all characters in the string. The rbearing
member is set to the maximum R.

For fonts defined with linear indexing rather
than 2-byte matrix indexing, each XChar2b structure is interpreted as
a 16-bit number with byte1 as the most significant byte. If the font has
no defined default character, undefined characters in the string are taken
to have all zero metrics.

Characters with all zero metrics are ignored. If
the font has no defined default_char, the undefined characters in the string
are also ignored.

XQueryTextExtents and XQueryTextExtents16 can generate
BadFont and BadGC errors.